Process of refining dimethylformamide



United States Patent PROCESS or nnrrynqn nrM rnr/rranMAMrnE Ernst Pirot, Erlenbach (Main), Germany, assignor to Vereinigte Glanzstor'f-Fabriken Alrtiengesellschaft, Wuppertal-Elberfeld, Germany, a joint-stock company under German law No Drawing. Application November 2, 1953 Serial No. 389,878

Claims priority, application Germany November 8, 1952 2 Claims. (Cl. 202-56) This invention relates to a method of refining dimethylformamide, a substance which plays an important role in the production, by spinning, of artificial fibers.

It is an object of this invention to provide a simple process for purifying or refining crude dimethylformamide by freeing it from impurities which greatly impair its usefulness as a spinning solution.

As is well known to persons skilled in the art of artificial fiber production, when dry-spinning polyacrylonitriledimethylformamide solution and recovering the dimethylformamide, a product is obtained which, owing to the relatively high working temperatures which exceed 150 C., has to a certain extent be decomposed by cracking and contains by-products such as for instance dimethylamine and even ammonia. The normal Way of dealing with such crude mixture by distilling it under pressure or in a vacuum does not lead to a satisfactory separation of these by-products from the dimethylformamide. If, however, the refined product still contains traces of dimethylamine or ammonia, it will, if used again as spinning solu tion, being about a strong discoloration and gelatinisation of the material. Even as little as 0.1% dimethylamine in the solution lead to so strong a gelatinisation as to create disturbances in the spinning process. Hitherto no means were known for doing away with these traces of dimethylamine.

I have now found a very simple way of getting rid of this impurity and altogether regenerating the dimethylformamide in pure condition. I achieve this by subjecting the raw product to distillation together with up to 20% of an aromatic compound which boils at a lower temperature than the dimethylformamide and more es- .pecially benzene, toluene and xylene.

In practicing my invention, I may for instance proceed as follows:

Example 1 To 90 parts by volume crude dimethylformamide were added 10 parts benzene and the mixture was fractionated under normal pressure and slowly heating from up to C. At first benzene, containing the amine present and traces of water, distilled over and further distillation under a vacuum yielded pure dimethylformamide which was now driven over at 60 C. under a vacuum of 28 Torr.

Example 2 To 90 parts by volume crude dimethylformamide were added 6 parts benzene and 4 parts of a light benzine boiling between 80 and 90 C. and the mixture was subjected to fractionation. Here again the traces of dimethylamine were driven over first with traces of water, the temperature being slowly raised from 65 to 80 C. Further distillation at 60 under a vacuum of 28 Torr yielded an altogether pure dimethylformamide.

Example 3 To parts by volume crude dimethylformamide were added 15 parts toluene and the mixture distilled at 65-69 C. under a vacuum of 200 Torr. The first runnings contain in the toluene also such quantities of water and dimethylamine, but then pure dimethylformamide distills over at a temperature of 72 C. under a vacuum of 50 Torr.

Example 4 parts of crude dimethylformamide are mixed with 10 parts technical xylene, boiling at 136-l40 C. and the mixture fractionated at 6572 C. under a vacuum of 80 Torr. The first runnings again contain the impurities and a perfectly pure dimethylformamide is obtained at 72 C. under a vacuum of 50 Torr.

Various changes may be made in the proportions of the materials and the temperatures and pressures used without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of purifying dimethylformamide contaminated with dimethylamine and ammonia which comprises admixing to the dimethylformamide, up to 20 percent by weightof the dimethylformamide, of an aromatic compound selected from the class consisting of benzene, toluene and xylene, and subjecting the mixture thus obtained to a fractional distillation whereby to remove any dimethylamine and ammonia leaving purified dimethylformamide as a residue.

2. The method of claim 1, wherein a small quantity of a light benzine boiling within the range of 70 to 90 C Great Britain Jan. 21, 1941 is added to the mixture prior to the fractional distilla- 

1. THE METHOD OF PURIFYING DIMETHYLFORMAMIDE CONTAMINATED WITH DIMETHYLAMINE AND AMMONIA WHICH COMPRISES ADMIXING TO THE DIMETHYLAMINE AND AMMONIA WHICH COMCENT BY WEIGHT OF THE DIMETHYLFORMAMIDE, OF AN AROMATIC COMPOUND SELECTED FROM THE CLASS CONSISTING OF BENZENE, TOLUENCE AND XYLENE, AND SUBJECTING THE MIXTURE THUS OBTAINED TO A FRACTIONAL DISTILLATION WHEREBY TO REMOVE ANY DIMETHYLAMINE AND AMMONIA LEAVING PURIFIED DIMETHYLFORMAMIDE AS A RESIDUE. 